There are many scientific challenges that need to be overcome to manufacture carrier based dry powder inhaler (DPI) products that are safe and therapeutic for treating respiratory diseases. Of these, controlling the manufacture and critical quality attributes (CQAs) of raw materials (both the active pharmaceutical ingredient and excipients) is critical to the successful development of a safe and efficacious DPI product. In this proposal, we seek to determine how primary crystallization and secondary processing of APIs directly influence formulation structure and product functionality of single component and combination based DPI products. The major research objective is to identify and provide a science based understanding of the CQAs of primary and secondary processed APIs. A greater understanding of this relationship between primary crystallization, its CQAs and their influence on surface interfacial properties of micronized APIs, will provide the necessary science and tools to enable greater control of product safety, efficacy, potency, quality and performance. The exploration into the relationship between the physicochemical properties of primary crystals, surface interfacial properties of secondary processed micronized API and the CQAs of these particles will aid the FDA to direct both brand and generic industries to define quality and functionality in DPI drug products.